1. Field of Invention
The invention relates to a rollover determination system for determining a possibility of a rollover of a vehicle. The rollover determination system is mounted on a vehicle as a preprocessing system of an occupant protection device such as a side airbag and is adapted to activate the occupant protection device immediately and appropriately in the event of the vehicle rollover.
2. Description of Related Art
A rollover determination system for determining a rollover of a vehicle is disclosed in Japanese Laid-open Patent Publication No. 2000-9599. In this system, it is determined whether the vehicle is in a rollover state at an earlier stage on the basis of not only a rotational angular velocity in the longitudinal direction of the vehicle, but also a roll rate that represents a lateral acceleration of the vehicle.
The aforementioned rollover determination system uses the lateral acceleration as well as the rotational angular velocity for the detection of a rollover of the vehicle. This makes it possible to activate an occupant protection device so as to protect the occupant of the vehicle in the event of the rollover.
Upon collision of the vehicle at its front portion (front-end collision), an air bag for the front-end collision is deployed based on a detected value of an acceleration sensor (a G-sensor) disposed in the vehicle. The acceleration sensor detects longitudinal acceleration of the vehicle.
Recently, a safing function has been added to the determination system for the deployment of the airbag for the front-end collision so as to prevent the airbag or the like from being activated by mistake. Assuming that deployment of the airbag is determined on the basis of a signal sent from a single G sensor, the airbag may be deployed in accordance with a wrong determination made on the basis of the error signal of the G sensor owing to noise, or failure of the G sensor. The safing function is added to the collision determination system in order to prevent undesired activation of the occupant protecting device in accordance with the wrong determination.
For achieving the above-described safing function, for example, regarding front-end collisions, a mechanical safing sensor is provided at a central portion of a vehicle in addition to the G sensor provided in a front portion of the vehicle so that the front-end collision is detected using values sent from a plurality of sensors.
The aforementioned safing function is applicable to a side collision of the vehicle. Detected values of a plurality of lateral acceleration sensors (G sensors) mounted in different portions of the vehicle are combined, based on which the side collision of the vehicle can be accurately detected.
In the event the vehicle is rolled over, the occupant is hit against the side of a passenger compartment. Accordingly the occupant protection device, for example, the side airbag, curtain shield airbag, seat belt pretensioning device and the like is activated. Like the front-collision, it is undesirable that the occupant protection device for the rollover is activated faultily.
It is preferable that the safing function be operated during determination of the vehicle rollover as in the case of the front-end collision. Any satisfactory proposal, however, has not been made yet with respect to the aforementioned function. There has been proposed to prevent faulty activation of the occupant protection device for the front-collision or the side-collision by operating the safing function. The technology for operating the safing function for preventing faulty activation of the occupant protection device has not been considered to a satisfactory level.
Furthermore it is preferable that determination of the vehicle rollover be made 20 on the basis of the lateral acceleration as well as the roll rate. However, any proposal with respect to the safing sensor used for determining the vehicle rollover has not been made yet. The mechanical sensor may be used as the safing sensor used for detecting the rollover as in the case of the front-collision. The mechanical sensor that is capable of accurately determining the vehicle rollover has not been introduced yet. Use of the safing sensor with a response lag may delay the determination of the vehicle rollover.
Meanwhile, the safing sensor with excessively high sensitivity may be brought into ON state frequently even when the vehicle is in a normal running state, failing to perform the intended safing operation. .